Add new Button and IconButton components (#3448)

This PR adds new `Button` and `IconButton` components built on top of
our new button abstractions.

Both of these buttons are built from the common `ButtonLike` base, and
implement the `ButtonCommon` (name TBD) trait in order to provide a
common interface.

There are still some visual tweaks that we'll need to make to the new
buttons, but those should be straightforward to make after we land this.

Release Notes:

- N/A

crates/ui2/src/components/disclosure.rs

@@ -39,8 +39,8 @@ impl RenderOnce for Disclosure {
                 false => Icon::ChevronRight,
             },
         )
-        .color(Color::Muted)
-        .size(IconSize::Small)
+        .icon_color(Color::Muted)
+        .icon_size(IconSize::Small)
         .when_some(self.on_toggle, move |this, on_toggle| {
             this.on_click(move |event, cx| on_toggle(event, cx))
         })